A new study of cleft palate in horses shows that while it leads to euthanasia in half of affected horses, the condition is, thankfully, extremely rare.
Cleft palate is a congenital defect in the roof of the mouth, leading to a split down the center of the structures. The condition can involve the hard palate (the bony front portion of the roof of the mouth), the soft palate (the softer back portion of the roof of the mouth), or both.
“The causes of cleft palate in horses are poorly understood and believed to be multifactorial,” says Sarah Shaw, DVM, of Texas A&M University. “Causes may include genetic factors, exposure to ionizing radiation or teratogens0, vitamin and mineral deficiencies, and the administration of some drugs during pregnancy.”
In a retrospective study, Shaw’s team found that the incidence of cleft palate in horses was only 0.04 percent among horses admitted to the university clinic from 1988 to 2011, with a total of 28 cases identified. Half of those were foals less than 2 months of age when the diagnosis was made, 21 percent were between 2 months and one year, and 29 percent were older than one year.
Shaw says diagnosis may be delayed because of the unseen nature of many cases. “No primary palate defects [those that involve the nostrils and lips] were identified in this study. All of the defects involved either the hard and/or soft palate.” The most common defects, she adds, affect the rear two-thirds of the soft palate, meaning they are not outwardly visible and are found only during an endoscopic exam of the pharynx.
Even without visible signs of the defect, there are usually other indications of palate problems. “Most commonly, foals with cleft palate will demonstrate dysphagia [difficulty eating and swallowing] that results in bilateral nasal discharge of milk,” Shaw says. “Older animals with cleft palates may have persistent nasal discharge, cough, or have a history of pneumonia or respiratory infections.”
Eleven percent of the study horses underwent surgical repair of their cleft palate, 4 percent received only supportive care (such as treating resulting respiratory infections) and 32 percent had no treatment. Of the 28 cases of cleft palate, 46 percent survived to be discharged from the hospital.
About 50 percent of the horses with cleft palate were euthanatized, a rate that might reflect concern over the potential complications of treatment. “Cleft palates can result in aspiration pneumonia,” says Shaw, “which can be life-threatening, so surgical correction is often recommended. However, surgical complications such as dehiscence [reopening] of the suture line, osteomyelitis [infection] of the mandible, and chronic dysphagia are reported to occur in up to 90 percent of attempted repairs. Yet, in this study, most cases that were euthanatized were not treated surgically. The likelihood of complications and the cost of surgical and medical therapy may have influenced owners’ decisions.”
On a more positive note, the researchers identified a few adult horses who were managing quite well despite a cleft palate. “None of these horses had involvement of the hard palate, and it is possible that they had more minor defects of the soft palate for which they were able to compensate,” says Shaw. “A number of these horses had careers as riding horses or racehorses without any apparent deleterious effects of their cleft palate.”
Reference: “Clinical characteristics of horses and foals diagnosed with cleft palate in a referral population: 28 cases (1988-2011),” Canadian Veterinary Journal, July 2015